Pumice stone vs muriatic acid for pool tile calcium scale: Start with the pumice stone for light buildup, switch to acid for thick scale.

Pumice stone is cheap, safe, and won’t scratch glazed ceramic or glass tiles — just wet and rub. For thick or crusty scale, use diluted muriatic acid (10:1 water to acid), let it fizz 30 seconds, scrub with nylon, and rinse. Test acid on an inconspicuous spot first, especially on natural stone or salt-finished tiles. Avoid wire brushes, razor blades, or harsh pads — they scratch. Never mix acid with chlorine or other pool chemicals.